doctype
html
    head
        meta(charset="utf-8")
        title jade测试页面
        style.
            div {width:100px;height:100px;background:red;text-align:center;line-height:100px;float:left;margin:10px auto;}
            div.last {clear:left;}
    body
        -var a=0;
        while a<12
            if(a%4==0 && a!=0)
                div.last #{a++}
            else
                div=a++

